Film casting base



Patented May 25, 1937 UNITED STATES PATENT OFFICE FILM CASTING BASE No Drawing. Application April 13, 1935, Serial No. 16,217

1 Claim.

This invention relates to a base for the casting thereon of film forming solutions which are to dry or set into transparent films of uniform thickness having smooth surfaces free from imperfections, blemishes, scratches and the like.

More specifically this invention relates to a carrier band or casting drum having a built-up smooth surface thereon adapted to receive solutions of rubber hydrohalide materials for the in formation of rubber hydrohalide films of uniform thickness and a high degree of transparency.

It has heretofore been proposed to use various types of metal drums or endless bands having if) the surfaces thereon in a highly polished condition to provide a glass-like finish for the films that are cast thereon. These surfaces have been built up by the lamination of various types of metal or by the electrodeposition of various metals 20 such as nickel, chromium, copper and the like on cast iron drums. In the casting of rubber hydrohalide film forming solutions, however, it has been found necessary to protect the metal surface with a coating of some material that is 5 not dissolved by the solvents of the film forming solution, does not corrode or oxidize when exposed to the surrounding atmospheric conditions and provides a film surface with a high degree of brilliance. This coating, furthermore, should (1') not transmit any slight imperfections or blemishes in the metal surface.

I have now provided a film casting base composed of an endless flexible band or a rigid drum or wheel of such metals as copper, brass, steel,

3:, iron and the like or chromium plated, nickel plated or the like metal plated surfaces having a casting surface of gelatine adhesively anchored thereon.

It is, then, an object of this invention to form 41) a casting base for film forming materials having a metal foundation and a smooth brilliant casting surface anchored thereon.

Another object is to build up a brilliant inert casting surface on a metal support. 3 Another object is to form a metal casting band or drum with a gelatine surface firmly bonded thereto.

In accordance with my invention the metallic drum or band is first polished and ground to a uniform smoothness. The smooth metallic surface is next washed with an organic solvent such as naphtha, benzol or the like to remove dirt and grime therefrom. This organic solvent washing operation is then followed with a further washing of the metallic surface with a solution of tri-sodium phosphate, ordinary soap on like grease dispersing agents to further clean the surface. A 5% solution of tri-sodiu n phosphate is preferable for this second washing operation.

After the washing operation with the grease 5 dispersing agents the metallic surface is further washed with water and dried. After the water washing operation the surface is again washed with phosphoric acid. The phosphoric acid wash is preferably repeated at least twice. For this wash I prefer to use a 5% solution of phosphoric acid although stronger or weaker concentrations may be used if desired.

After the final phosphoric acid wash the metallic surface is next dried and a liquid adhesive 16 such as glue is then coated over the washed surface. I prefer to use liquid fish glue and apply the same by the aid of a felt wick. The fish glue is readily wicked onto the metallic surface and a preferable solution is made up of two 20 parts of Water and one part of fish glue. It is dried on the metal surface at low temperatures and after the first coating has thoroughly dried, a second coating is preferably applied in the same manner.

When the second coating of the glue is thor-- oughly dry, a solution of gelatine is then coated thereover to form the casting surface. The application of the gelatine coating onto the glue coated metal surface should be very carefully handled to prevent the uneven distribution of the gelatine and to prevent the formation of air bubbles and the like in the casting surface. For this reason the following procedure is recommended. 5

The gelatine coating can be made of any commercial type of gelatine. However, a calfskin stock gelatine is preferred. This type of gelatine has a jell strength of about 283 grams; a viscosity of 43 millipoises and a pH of 6.4 determined according to standard glue testing specifications. 600 grams of this gelatine are soaked in 1200 grams of cold water for a period of about six hours or until the gelatine is completely swelled. The thus soaked gelatine is then melted 45 and dissolved on a water bath at a temperature of 120 grams of glycerin and 120 grams of alcohol are then thoroughly stirred into the. gelatine solution.

The presence of glycerin in the solution acts 50 as a humidifier and plasticizer preventing the resulting gelatine film from drying out and cracking. Other hygroscopic agents may be used in place of glycerin, such as water soluble parafiin glycols and the like. The alcohol in the solution speeds up the drying of the gelatine.

-Other low boiling solvents that are miscible with water may be used in place of alcohol.

The thus prepared gelatine solution is then poured into a container which has an opening on the bottom to permit the drawing off of the gelatine solution. This container with the solution therein is placed in a water bath at C. for a period of about an hour in order to permit any air bubbles present in the solution to rise to the surface of the container. After the solution has stood in the container for a period of time sufficient to permit the removal of all air bubbles therefrom, the temperature of the water bath is reduced until the gelatine solution has reached a temperature of about 47 C. At this temperature the solution is cast onto the metal surface of the belt having the glue coating thereon as described above. The gelatine coating is then dried slowly at a temperature of approximately F. After the drying operation the resulting surface can be subjected to much higher temperatures'without damage.

The provision of a brilliant surface film of gelatine on the metal carrier band makes it possible to provide brilliant casting surfaces on metallic bands or drums without subjecting the metallic surface to the action of the solvents in the film forming solutions that are cast thereon. Furthermore the built-up casting surface can be readily soaked off of the metal band or drum after it becomes worn or damaged and a new brilliant surface may be formed thereon without the necessity of replacing the metal band. This, of course, effects a large saving because heretofore when the metal casting band or drum became damaged it was necessary to dismantle the casting machine and replace the band or drum. The worn or damaged band or drum then had to be resurfaced either by grinding or polishing or by electroplating a finishing surface thereover. Furthermore the polishing of metal surfaces does not permit the formation of a perfectly smooth and brilliant surface that is free from imperfections because during the polishing operation small scratches and abrasions are always formed. These abrasions may only be of microscopic size when the band or drum is first placed on the casting machine but continual casting of film forming solutions thereon gradually increases the size of the scratches and abrasions until they assume proportions which are sufficient to damage the transparency of the film formed thereon.

While the film casting base of this invention is preferably used for receiving solutions of rubber hydrohalides in solvents such as ethylene dichloride, benzol, toluol, xylol, it is to be understood that other film forming solutions which do not dissolve gelatine may also be used.

I am aware that numerous details of the process may be varied through a wide range Without departing from the principles of this invention, and I, therefore, do not purpose limiting the patent granted hereon otherwise than necessitated by the prior art.

Having now described my invention, I claim:

A film casting base comprising a flexible metal band, a coating of fish glue on a surface of said band, and a film of gelatin spread over said fish glue coating to provide a smooth surface for coating films thereon, said smooth surface being firmly anchored to the band by said fish glue coating.

FLOYD E. WILLIAMS. 

